It is well known that emission properties of phosphors vary in accordance with temperature. This correlation has been used to devise various types of thermometry hardware. For example, surface temperature of a rotating flywheel has been measured by inducing fluorescence from a pulsed nitrogen laser in a material that includes lanthanum oxysulfide doped with europium. The temperature dependence of the phosphor emission has been shown both in amplitude and lifetime changes. With a pulsed laser as the stimulating source, either the ratio of two emission line intensities (amplitudes) or the lifetime of some selected line can be used to determine the temperature.
In the field of nuclear reactor engineering, the interactions of neutrons with nuclei are important to the release of nuclear energy in a form capable of practical utilization. Inelastic neutron collisions do not occur below energies of about 0.1 Mev, but elastic collisions between neutrons and nuclei will be effective in slowing down the neutrons until their average kinetic energy is the same as that of the atoms of a scattering medium. This energy depends on the temperature of the medium, and is thus referred to as thermal energy. Neutrons whose energies have been reduced to values in this region are designated "thermal neutrons".
Phosphors have been used to measure thermal neutron flux. A mixture of boron-containing plastic and ZnS(Ag) phosphor has been used to provide a slow-neutron scintillator. A slow neutron passing through the scintillator is captured by a B10 nucleus. The resultant energetic alpha and lithium particles reach a ZnS(Ag) granule with sufficient residual energy to cause a scintillation. Light from the scintillation travels to the photomultiplier photocathode and reaches it with sufficient intensity to cause a recognizable pulse at the anode. The slow-neutron scintillators have been made by using a transparent bioplastic mold cast from a negative steel mold. In use, the surface of the scintillator faces a photomultiplier, while the opposite surface is covered with aluminum foil or other light reflective coating. See, for example, "High Efficiency Slow-Neutron Scintillation Counters", NUCLEONICS, by K. H. Sun et al. (July, 1956).
The extreme environment of some nuclear reactor cores, with temperatures in the range of 1,000.degree. C., presents a difficult problem for sensing both temperature and neutron flux. A need exists for an improved sensor capable of simultaneously measuring both neutron flux and temperature.